The present invention relates to an electron beam illumination device used in the lithography process in the manufacture of semiconductor devices, and an exposure apparatus with the electron beam illumination device.
Conventionally, in the lithography process in mass-production of semiconductor devices, an exposure technique based on light exposure is used. However, in recent years, as semiconductor devices continue to have a higher degree of integration, the line width in the device is shrinking. Especially, in semiconductor memory devices such as 1 G and 4 G DRAMs the line width is 0.2 .mu.m or less, which is considerably small. As an alternative exposure technique to light exposure, an exposure apparatus using electron beams with higher resolution is beginning to gain attention.
However, existing electron beam exposure apparatuses mainly use a Gaussian method and variable forming method using a single beam, and require much time in the lithography process in the manufacture of semiconductor devices. Hence, owing to low productivity of semiconductor devices, the electron beam exposure apparatus is used in only limited applications that particularly require its excellent resolution performance, such as mask drawing, study and development of VLSIs, exposure of ASIC devices that are produced in small quantity, and the like. For this reason, improvements in the productivity of semiconductor devices are a major problem upon applying the electron beam exposure apparatus to the mass-production of semiconductor devices.
As a means for solving the above problem, in recent years, so-called stepping transfer has been proposed. FIG. 17 is a perspective view showing an exposure apparatus using conventional stepping transfer. In the stepping transfer, as shown in FIG. 17, circuit patterns 101 to be repetitively formed on a wafer 102 are formed into cells, thereby improving productivity upon drawing interconnect patterns on the wafer 102 by exposure.
Since the maximum region of the wafer that can be exposed at one time using the stepping transfer is as small as about several .mu.m as in the variable forming method, a plurality of (e.g., two or three) deflectors must be used, and chromatic aberrations, distortion, and the like produced upon deflection must be removed using an MOL (movable objective lens system) to obtain a wider exposure region. In order to improve the productivity of semiconductor devices, it is again required to broaden the exposure region. However, it is hard to broaden the exposure region while maintaining both high overlay accuracy of exposure regions and high exposure resolution. For example, when the overlay accuracy of exposure regions ranges from 20 to 30 nm, and the exposure resolution is 0.2 .mu.m or less, the exposure region can be broadened to about 1 mm by deflection.
As described above, in the conventional electron beam exposure apparatus, since the region of the wafer that can be exposed at one time is smaller than the entire region to be exposed on the wafer, means for scanning an electron beam or reciprocally moving a stage that carries a wafer or exposure mask is used to expose the entire region to be exposed on the wafer.
However, as described above, since the exposure region of the electron beam is smaller than the region to be exposed on the wafer, the wafer must be reciprocally moved many times or the electron beam must be repetitively scanned to expose the entire region to be exposed on the wafer. For this reason, a longer wafer exposure time is required than a light exposure type exposure apparatus.
In order to shorten the wafer exposure time, at least one of means for increasing the scanning speed of the electron beam or the moving speed of the stage that carries the wafer or exposure mark, and means for broadening the exposure region of the electron beam is required.
However, with the means for increasing the scanning speed of the electron beam or the moving speed of the stage, the amount of irradiated electron beam may become short, and the wafer may not be sufficiently exposed. In such case, the irradiation intensity of the electron beam may be increased, but then the exposure image is blurred.
On the other hand, with the means for broadening the exposure region of the electron beam, the electron beam must be irradiated at a uniform intensity within the exposure region so as to obtain a uniform line width on the wafer. However, the exposure region on the wafer by a single electron beam is as small as several .mu.m, and even when a conventional emittance LaB6 electron gun having a deflector is used, the emittance value (the product of the crossover and electron beam output angle) is as low as about several 10 .mu.m mrad. For this reason, when a conventional electron beam illumination system is used, it is difficult to further broaden the exposure region and to uniformly irradiate the electron beam onto that exposure region.